An optical technique for measurement of material properties in the tension Kolsky bar

In this paper, a simple and effective technique is described for measurement of the viscoplastic tensile strains of specimens in the tension Kolsky bar experiment. The technique uses a Laser Occlusive Radius Detector (LORD) to directly measure the local diametral strain. To verify the accuracy of this technique, comparative tests of an A359 aluminum alloy were performed in which the strains in the specimens were simultaneously determined using the LORD approach and on-specimen strain gauges. Full numerical simulations of the tension Kolsky bar experiment were also performed for a variety of specimen geometries and material properties to evaluate the domains of accuracy of each measure of specimen strain. The experimental and numerical results show that (i) the strain measured using the LORD approach is in very good agreement with that measured using on-specimen strain gauges; (ii) the LORD approach continues to provide strain measurements after failure of the on-specimen strain gauges; (iii) the strain measured using conventional approaches is different from the strain measured using either the LORD or the on-specimen strain gauges.